1. Field of the Invention
The present invention relates to a method of impregnation treatment for foods by which foods are impregnated with a liquid component or a gas component.
The present invention also relates to a method for obtaining vitamin C-containing eggs by impregnating eggs with a vitamin C component, and a method for obtaining pidan-like eggs by impregnating eggs with an alkali component.
2. Description of the Prior Art
There are a variety of foods known as impregnated with seasonings or the like. These foods are obtained by such a cooking method as boiling foods, such as vegetables, meats and fishes, in hot water containing seasonings, or soaking the foods in seasonings.
However, boiling of foods often results in hardened or softened foods due to the heat and inevitably causes the foods to have a different eating texture from that before the heating. Also, boiling of foods requires a long time to complete sufficient impregnation of the foods with seasonings, and it necessitates a large amount of heat energy to conduct the heating.
To shorten the time required to flavor foods by boiling, JP-B-7(1995)/112453 proposes a flavoring method by preparation in a depressurized cooker, in which a cooker containing cooking ingredients and seasoning components is depressurized to impregnate the ingredients with the flavor quickly into the inside. However, this method only achieves, when water-rich ingredients are depressurized as being soaked in a seasoning liquid, the substitution of the moisture in the ingredients with the seasoning liquid due to the difference of osmotic pressures, and remains unsatisfactory in terms of shortening of the flavoring time.
Meanwhile, soaking of foods in seasonings, although allowing foods to be impregnated with seasonings at ordinary temperature or low temperatures, requires a further longer time to complete deep impregnation of the foods with seasonings than by the boiling method.
In order to impregnate foods with liquids by a method other than these conventional cooking methods, it has been proposed (in JP-A-4(1992)/287665) that beef can be injected with a liquid and massaged to disperse the liquid in the tissues. This method, however, has problems that the uniform dispersion of the liquid in the tissues is difficult to attain and that the massage may destroy the tissues. Furthermore, such a method, inconveniently, cannot be applied to foods lacking in flexibility.
Also, JP-A-6(1994)/205638 proposes a method for preventing oxidation in production of pickles, in which a container containing pickles is depressurized to pressurize the pickles inside the container by the pressure difference, thereby creating a state where the pickles are being pressed by a weight, and simultaneously the oxygen around the pickles is removed to prevent oxidation. This method, which produces pickles in a so-called vacuum-packed state, is almost at the same level in terms of impregnation effects as that using a weight, and needs a long time for impregnation with seasonings.
As such, a simple method for impregnating foods with a liquid component in a short time is strongly demanded.
Moreover, it has been conventional to substitute a gas in a preservative environment for foods, which is air typically, with other gas; for example, preserving foods in packages filled with nitrogen. It has been unknown, however, to impregnate foods with a gas by substituting a gas or a liquid in the food tissues with other gas.
Meanwhile, eggs, such as chicken eggs and quail's eggs, are known to contain well-balanced nutritive components, such as proteins, lipids and minerals, and to be high in nutritional value among other foods. Eggs contain most of essential nutrients for humans except vitamin C. Therefore, the appearance of vitamin C-containing eggs is desired.
Examples of unshelled eggs (eggs with eggshells) known as impregnated with nutritive components, seasonings and other components include smoked eggs, which are prepared by boiling unshelled eggs and smoking them, and pidans, which are prepared by soaking eggs in a strongly alkaline paste to denature the proteins in the eggs into a gelled state. Also known are nutritionally enriched eggs produced by chickens or the like that have been fed with feedstuffs nutritionally enriched by, for example, iodine and fatty acids.
However, no eggs have been obtained as being enriched in vitamin C, the missing nutrient, and production of vitamin C-containing eggs by feeding chickens or the like with feedstuffs enriched in vitamin C has not been realized because, in such cases, the vitamin C in the feedstuffs is rarely transferred to the eggs.
It has been concerned, even if the vitamin C is successfully added in the eggs, that the eggs will have a destroyed flavor due to the strong acid taste of ascorbic acid.
On the other hand, pidans are a traditional Chinese food produced by processing duck eggs or the like as ingredients, and are widely known today as a food high in nutritional value and excellent in preservative quality. The pidans generally consist of a brown, gel-like albumen having transparency and a dark-green, soft-boiled or hard-boiled conditions of egg yolk, and have a sulfurous or ammonia smell.
The pidans can be prepared by, for example, soaking ingredient eggs in a strongly alkaline liquid containing salt for about 1 to 3 months, coating the resulting eggs with clay or mud and then with hull chaffs, and leaving the eggs at rest for about a half-month to 1 month. It is also known that the pidans can be prepared by coating ingredient eggs thickly with a clay-like mixture of sodium carbonate, peat mosses, salt, limestone, water, etc, coating the outside of eggs with hull chaffs, placing the eggs in a pot or a can, and leaving the eggs at rest in the sealed pot or can for about 3 to 6 months. It is also known that, in this production of the pidans, the color of pidans can be controlled by addition of a tea broth.
As mentioned above, the conventional pidans, although excellent in preservative quality, need 3 to 6 months, occasionally nearly 1 year for preparation. Accordingly, producers need to provide a place to store the pidans in preparation at rest over a long period of time.
Also, with the recent development of distribution and refrigerator storage technique, foods are required to have a short preparation time rather than excellent preservative quality.
Under these circumstances, there have been demanded a method for readily impregnating foods with a liquid component or a gas component in a short time, a method for efficiently impregnating eggs with vitamin C or a derivative thereof, and a method for producing pidan-like eggs by efficiently impregnating eggs with an alkali component.
The present inventors made an earnest study in light of such circumstances, and found that foods can be favorably impregnated in the tissues thereof with a liquid or a gas in a short period of time by vacuum treating the foods and contacting them with a liquid or a gas, or by cooling the foods in contact with a liquid component. The inventors also found that vitamin C-containing eggs and pidan-like eggs can be favorably prepared by the above method. The present invention has been completed with such findings.